Automated meter reading (AMR) systems are designed to retrieve consumption data from utility meters, such as gas, water, and electric meters. Two such systems are described by U.S. Pat. No. 6,333,975 and U.S. Patent Application Publication No. 2002/0109607 A1, both of which are herein incorporated by reference. AMR systems employ a variety of techniques for collecting data from transceivers installed at the meters, commonly referred to as “endpoints”, including telephone connections, radio signals, optical signals, inductive probes, and direct electrical connections.
Radio based systems often employ a mobile reader device, carried either by a person on foot or by a vehicle, to periodically travel throughout a utility's service area and read the endpoints. In a first approach, the mobile reader device transmits a “wake-up” call to the endpoints. This technique is generally used for battery-operated endpoints which typically employ an ultra-low current receiver that listens for the wake-up call from the reader device. Upon “hearing” the wake-up call, the AMR endpoint transmits a data message, including meter consumption data, that is received by the mobile reader device. In a second approach, often referred to as “bubble-up”, the AMR endpoints do not listen for a wake-up call, but instead periodically transmit a data message—often several times per second. A reader device then simply listens for the transmitted messages.
A second approach utilizes an existing public network, such as a cellular telephone network or a two-way paging network, to collect data from the endpoints. However, this method tends to be expensive because it requires more complex endpoints and network providers generally charge a substantial monthly fee per endpoint.
Another approach employs a geographically fixed system, or network, of reader devices that retrieve data messages from the AMR endpoints and forward them to some type of host system. Such a system can employ a wake-up type system transmitting wake-up calls to the AMR endpoints or receive data from bubble-up type endpoints.
When a network of reader devices is employed to read the endpoints, there is a substantial cost associated with installing each of the reader devices, or nodes. Since the number of nodes required is related to the transmission range of the endpoints, one way of reducing network costs is to increase the transmission range of the endpoints. The farther an endpoint can transmit, the fewer the nodes that are required. In fact, the number of network nodes required is inversely proportional to the square of the endpoint transmission range. Therefore, if the endpoint transmission range can be doubled, the number of network nodes can be reduced by a factor of four. Also, because of the costs associated with installing network nodes, it is often desirable for utilities to begin an AMR system “rollout” by first reading endpoints with a mobile-type reader and later upgrading to a fixed network system.
AMR systems generally transmit a meter's consumption data, or reading, via the endpoint either when commanded by a reader or periodically on a bubble-up basis. Typically, a customer's bill is based on the value of the metered product, such as electricity or gas, at the time the meter is read. However, given current economic conditions regarding energy and water, utilities are becoming increasingly interested in adjusting the price of the product as a function of the time when it was consumed, since an electric rate, for instance, might be more expensive at time of peak electrical usage. This is generally referred to as a time-of-use billing system.
However, because conventional AMR endpoints typically provide a single consumption value at the time a meter is read, it is generally not possible to use a mobile reader device to read a meter's usage as a function of time. While this is not a problem for a network system, which can continuously accumulate meter readings and derive a profile of usage versus time, such systems can be very costly.
Conventional AMR systems generally utilize very low current super-regenerative type receivers in the endpoint devices. Super-regenerative type receivers have a low sensitivity and are not able to receive data at rates much over sixty bits per second when running extremely low current. Furthermore, such receivers have a large bandwidth making them susceptible to interference. Conventional AMR systems often utilize an audio tone of around 30 Hz to wake-up the endpoints. The endpoints respond to the wake-up call by on-off keying an oscillator in the 902-to-928 MHz ISM band. To avoid signal collisions and to meet FCC requirements, the endpoints “frequency hop” the oscillator within the band. However, since the transmitter is not crystal-controlled, it is not known precisely at which frequency the endpoints will transmit.
One conventional high performance approach employed to overcome this shortcoming is to employ a reader having multiple receivers fix-tuned at every few hundred KHz across the band. One known reader system employs forty-eight receivers. Such a reader is expensive and bulky in size. Another approach is to employ a reader having a wideband receiver. While such an approach works, the wideband receiver is very susceptible to interference and is limited in sensitivity due to its wide bandwidth. Still other systems use narrower bandwidth sweeping-type receivers or FFT-based receivers. Such systems suffer from high cost, performance, or weight.